IMMUNOLOGY. IMMUNITY AND IMMUNIZING AGENTS 245 



Bacterial clumping or agglutinating phenomena are extremely interest- 

 ing as well as valuable in the diagnosis of disease. Upon this behavior of 

 bacteria depends the Widal typhoid fever test. If the serum of an animal 

 inoculated with the typhoid bacillus (antiserum) is added to a liquid cul- 

 ture or suspension of typhoid bacilli, the latter cease to move and after a 

 time become aggregated into irregular clumps or masses. The same 

 phenomenon is observed if instead of blood of a typhoid injected animal, the 

 blood of a typhoid fever patient is employed. The reaction is quite specific, 



FIG. 62. Illustrating receptors of the third order, or so-called amboceptors. This 

 serves to explain. the action of lysins (bacteriolysin, hemolysin, cell lysins, milk lysins, 

 etc.). The cell receptor (amboceptor) has two haptophore groups, one (e) capable of 

 uniting with a disintegrated substance as bacterial cell, blood-corpuscle, etc., (/) and the 

 other (g) having the power to combine with a complement (&). h is the haptophore 

 group of the complement (lysin) and z the zymotoxic group. Arnboceptors, lysin re- 

 ceptors and receptors of the third order mean the same thing. (Journal of the American 

 Medical Association, 1905, p. 1369.) 



though not absolutely so. That is, similar agglutinating phenomena are 

 produced by related bacilli, as the typhoid bacillus, the para-typhoid 

 bacillus and the colon bacillus. Many other bacteria, beside the colon- 

 typhoid group, are agglutinated by their respective antisera. In addi- 

 tion to diagnosing disease as in typhoid fever (the Widal test gives results 

 even before there are marked disease symptoms), the agglutinating phe- 

 nomena are useful in the identification of bacteria. The technic while not 

 difficult, calls for many precautionary measures and requires considerable 

 time and care to avoid erroneous conclusions. 



In 1897 Kraus found that when the germ-free filtrates from broth cul- 

 tures of bacteria were mixed with their respective antisera (serum from 

 animals inoculated with the specific bacteria) the formation of a white 

 precipitate occurred. The substance in the immunized serum which 

 causes the formation of the precipitate has been termed precipitin. Simi- 



